This application claims the benefit of French application serial no. 9816741 filed Dec. 31, 1998, which is hereby incorporated herein by reference, and which claims the benefit under 35 U.S.C. xc2xa7 365 of International Application PCT/FR99/03319, filed Dec. 30, 1999, which was published in accordance with PCT Article 21(2) on Jul. 13, 2000 in French.
The present invention relates to the field of telecommunications, especially microwave telecommunications, and relates more particularly to a telecommunications device with shaped electronic scanning arrays. It also relates to a telecommunications terminal in a satellite constellation system and to a wireless communications terminal for communicating with domestic appliances.
Hitherto, commercial telecommunications via satellite have been achieved almost entirely by geostationary satellites, which are particularly beneficial because of their unchanging relative positions in the sky. However, a geostationary satellite has major drawbacks such as considerable attenuations of the transmitted signals which are associated with the distance separating the user antennas of the geostationary satellite (about 36,000 kilometers, the corresponding losses then rising to about 205 dB in the Ku band) and transmission lags (typically about 250 ms to 280 ms) thus becoming clearly perceptible and annoying, especially for real-time applications such as telephony, video conferencing, etc. Furthermore, the geostationary orbit, located in the equatorial plane, poses a visibility problem for regions at high latitude, the angles of elevation becoming very small for the regions close to the poles.
The alternatives to employing geostationary satellites are:
the use of satellites in inclined elliptical orbit, the satellite then being almost stationary above the region situated at the latitude of its apogee for a duration of possibly up to several hours,
the implementation of satellite constellations in circular orbit, in particular in low orbit (xe2x80x9cLow Earth Orbitxe2x80x9d or LEO) or in mid-orbit (xe2x80x9cMid Earth Orbitxe2x80x9d or MEO), the satellites of the constellation flying past in turn within visibility of the user terminal for a duration of from some ten minutes to around one hour.
In both cases, the service cannot be provided permanently by single satellite, continuity of service demanding that several satellites fly over the service area one after another.
Document EP 0 598 656 A1 describes a frustoconical array antenna comprising elements radiating along cone generatrices. Such an antenna is intended for the tracking of targets. However, this antenna is only able to operate in a single frequency band.
The aim of the invention is to remedy the problem of the prior art.
To this end, the subject of the invention is a telecommunications device with electronic scanning arrays shaped over a first surface with complete or partial rotational symmetry, comprising:
a first array of first radiating sources arranged over the said first surface area in order to operate about a first central frequency, characterized in that, in addition, the said device comprises:
a second array of second radiating sources arranged over a second surface with rotational symmetry adjacent to the said first surface in order to operate about a second central frequency,
the first and second sources being placed such that a first source and a second source do not face a second source and a first source respectively, along a section normal to the first and second surfaces pointing to the first source and the second source respectively.
Thus the invention makes it possible to operate about two central frequencies and can be shaped according to its application. Such a configuration of radiating sources of the two facing arrays makes it possible to minimize the interactions between the facing sources. The invention has the advantage of proposing a device operating about two central frequencies (which amounts to having two different antennas) for virtually the same physical surface. In addition, the process for manufacturing the substrate forming the surface associated with such a device is simple since it only requires the formation of two flat substrates of surface areas corresponding to the deployment of the said first and second surfaces.
According to one embodiment, for each array corresponding to the said surfaces, the radiating sources are arranged according to M respective alignments linking a point oriented towards radiation space to a base opposite to the said point.
According to one embodiment, the said first and second surfaces are conical or partially conical. In this way, the device according to the invention makes it possible to track a moving element wherever it is in the radiation field of the device. Its conical shape means it is possible to cover a solid receiving angle of 360xc2x0 in azimuth and of 90xc2x0 in elevation.
In the present application, the term xe2x80x9celevationxe2x80x9d refers to an angle between the satellite and the local horizon while the term xe2x80x9cazimuthxe2x80x9d corresponds to a movement of the satellite in the plane orthogonal to the elevational movement determining an angle connecting the satellite to a local reference vertical.
When tracking a moving element by the device along the azimuthal plane, in order for steady tracking to be possible, at a current time t, on each array, the N alignments fed by the switch have Nxe2x88x921 alignments common with those fed at the previous feed time, a new feed time being defined by modifying the feed of at least one of the N alignments.
According to one embodiment, the radiating surface of each radiating source increases with the distance, along the alignment to which the said source belongs, separating the said radiating source from the said point, which makes it possible inter alia to compensate for the loss in signal level during its trajectory along the alignment.
According to one embodiment, the or one of the characteristic dimensions of the radiating surface of each radiating source and perpendicular to the corresponding alignment increases with the distance, along the alignment to which the said source belongs, separating the said radiating source from the said point.
According to one embodiment, the device according to the invention comprises, for each array corresponding to the said surfaces, first phase shifters combined with each source to control the phases of the said alignments relative to the sources.
According to one embodiment, the device according to the invention comprises:
a switch coupling the said 2M alignments of the said first and second arrays to N lines of an array of combiners/dividers, where N less than M, the said switch being capable of feeding N adjacent alignments of each array of sources at a given instant,
a controller to control the switch and the first phase shifters in order to tilt the radiation pattern resulting from the said 2N alignments along a first azimuthal direction and a second elevational direction, respectively.
In operation, on each array, the radiation from the surface formed by the array of N activated alignments does not correspond to that of a flat array, but to that of a curved array. Consequently, second phase shifters each control an additional phase shift of the N fed alignments, the said phase shift varying according to a phase gradient such that each source of N fed alignments is fed in an equiphase manner. Thus, the gain is optimized and the rise of the secondary lobes is reduced.
According to one embodiment, in order to communicate with a moving element, groups of N adjacent alignments are fed successively on each array of sources, each group being differentiated by a single alignment when tracking the said element.
According to one embodiment, each alignment comprises a succession of radiating sources, two radiating sources being separated by a first phase shifter.
According to one embodiment, one and the same phase shifter is common to several alignments such that it can adjust the phase of several sources.
According to one embodiment, one of the said first or second arrays is adapted to receive signals and the other of the said first or second arrays is adapted to transmit signals, such that the said device is able to operate in bidirectional mode.
According to one embodiment, the radiating sources comprise radiating patches.
The subject of the invention is also a telecommunications terminal in a satellite constellation system, characterized in that it comprises a device according to the invention above.
According to one embodiment, in order to continually exchange signals with a satellite over time, the said controller comprises storage means comprising a table of positions with time of a plurality of satellites of the satellite system. Since this solution is purely electronic, there is no scope for switching lags when switching reception from a first satellite to another.
According to one embodiment, each satellite position, at a given instant, in radioelectric radiation space of the device has corresponding co-ordinates (N, xcex94"PHgr"), where N corresponds to N adjacent alignments to one and the same array fed by the said switch and xcex94"PHgr" represents the phase shift introduced by the said first phase shifters to the sources of the N alignments.
According to one embodiment, the controller is connected to the receiving circuit of the device in order to measure a quality parameter of the received signal. Thus, where the quality parameter is not complied with, the controller controls the exchange of signals with a satellite of known position in radiation space where the quality criterion for the received signal is fulfilled. For example, the quality criterion is the level of signal received. According to another variant, the quality criterion can be the error rate detected in a demodulator located in an internal unit to which the processing circuit is connected.
The subject of the invention is also a wireless communications terminal to communicate with domestic appliances, characterized in that it comprises a device according to the invention.